/*
 * Copyright (C) 2011 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.testing;

import static com.google.common.base.Preconditions.checkNotNull;
import static junit.framework.Assert.assertEquals;
import static junit.framework.Assert.assertTrue;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;
import com.google.common.base.Equivalence;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.Lists;
import com.google.common.testing.RelationshipTester.ItemReporter;

import java.util.List;

/**
 * Tester for {@link Equivalence} relationships between groups of objects.
 *
 * <p>To use, create a new {@link EquivalenceTester} and add equivalence groups where each group
 * contains objects that are supposed to be equal to each other. Objects of different groups are
 * expected to be unequal. For example:
 *
 * <pre>{@code
 * EquivalenceTester.of(someStringEquivalence)
 *     .addEquivalenceGroup("hello", "h" + "ello")
 *     .addEquivalenceGroup("world", "wor" + "ld")
 *     .test();
 * }</pre>
 *
 * <p>Note that testing {@link Object#equals(Object)} is more simply done using the {@link
 * EqualsTester}. It includes an extra test against an instance of an arbitrary class without having
 * to explicitly add another equivalence group.
 *
 * @author Gregory Kick
 * @since 10.0
 */
@Beta
@GwtCompatible
public final class EquivalenceTester<T>
{
    private static final int REPETITIONS = 3;

    private final Equivalence<? super T> equivalence;
    private final RelationshipTester<T> delegate;
    private final List<T> items = Lists.newArrayList();

    private EquivalenceTester(Equivalence<? super T> equivalence)
    {
        this.equivalence = checkNotNull(equivalence);
        this.delegate = new RelationshipTester<>(equivalence, "equivalent", "hash", new ItemReporter());
    }

    public static <T> EquivalenceTester<T> of(Equivalence<? super T> equivalence)
    {
        return new EquivalenceTester<>(equivalence);
    }

    /**
     * Adds a group of objects that are supposed to be equivalent to each other and not equivalent to
     * objects in any other equivalence group added to this tester.
     */
    public EquivalenceTester<T> addEquivalenceGroup(T first, T... rest)
    {
        addEquivalenceGroup(Lists.asList(first, rest));
        return this;
    }

    public EquivalenceTester<T> addEquivalenceGroup(Iterable<T> group)
    {
        delegate.addRelatedGroup(group);
        items.addAll(ImmutableList.copyOf(group));
        return this;
    }

    /**
     * Run tests on equivalence methods, throwing a failure on an invalid test
     */
    public EquivalenceTester<T> test()
    {
        for (int run = 0; run < REPETITIONS; run++)
        {
            testItems();
            delegate.test();
        }
        return this;
    }

    private void testItems()
    {
        for (T item : items)
        {
            /*
             * TODO(cpovirk): consider no longer running these equivalent() tests on every Equivalence,
             * since the Equivalence base type now implements this logic itself
             */
            assertTrue(item + " must be inequivalent to null", !equivalence.equivalent(item, null));
            assertTrue("null must be inequivalent to " + item, !equivalence.equivalent(null, item));
            assertTrue(item + " must be equivalent to itself", equivalence.equivalent(item, item));
            assertEquals(
                    "the hash of " + item + " must be consistent",
                    equivalence.hash(item),
                    equivalence.hash(item));
        }
    }
}
